Method and apparatus for making multiple copies from an original

ABSTRACT

Apparatus is disclosed for making multiple copies from an original by forming a first temporary image from the original which temporary image is used to sequentially expose a plurality of photosensitive surfaces to form multiple images. Thus, while successive photosensitive surfaces are being exposed, a first original may be replaced in an exposure station with another original from which copies are to be made. Time delay is reduced since the original from which subsequent copies are to be made can be positioned in the exposure station while multiple copies are being made from a temporary image formed from the first original. The temporary image is formed on a photoconductiveliquid crystal sandwich by a first source of radiation to which the photoconductive layer is sensitive, and is projected by a second source of radiation which may be within another portion of the electromagnetic spectrum to which the photoconductive layer is not sensitive.

0 {AX (We i United Stat 7 [111 3,778,149 Fields 1 Dec. 11, 1973 METHODAND APPARATUS FOR MAKING Primary ExaminerSamuel S. Matthews MULTIPLECOPIES FROM AN ORIGINAL Assistant Examiner-Michael D. Harris Attorney-W.H. J. Kline et al.

[75] Inventor: Gary D. Fields, Parker, C010.

[73] Assignee: Eastman Kodak Company, [57] ABSTRACT Rochester,N.Yl

Apparatus is disclosed for maklng multiple copies I Filedi 1972 from anoriginal by forming a first temporary image [21 APPL NOJ 227,238 fromthe original which temporary image is used to sequentially expose aplurality of photosensitive surfaces to form multiple images. Thus,while successive photo- [52] US. Cl 355/16, 350/160 LC ensitivg urfacesare being exposed, a first Original [51] Int. Cl G03g 15/14 ay b r pla din an exposure station with another Field 0f Search 350/160 160 originalfrom which copies are to be made. Time delay 355/l6 is reduced since theoriginal from which subsequent copies are to be made can be positionedin the expol l References Cited sure station while multiple copies arebeing made from UNITED STATES PATENTS a temporary image formed from thefirst original. The 3.631049 2/1972 Rhodes 355 3 temporary image isformed a photoconductive- 3 610 732 10/1971 Mack 350/160 R liquidcrystal sandwich by a first source of radiation to 3,619,054 11/1971Goffe 355/16 which the photoconductive layer is sensitive, and is3,582,206 6/1971 Burdige 355/16 projected by a second source ofradiation which may OTHER PUBLICATIONS be within another portion of theelectromagnetic specy Liquid Crystal Eectrophotographic Display, toWhich the photoconductive layer is not sens|- 12 IBM Tech. DisclosureBul. 2135 (May 1970) 15 Claims, 1 Drawing Figure NO. OF 55w COUNTERSTATION 0R mass/la METHOD AND APPARATUS FOR MAKING MULTIPLE COPIES FROMAN ORIGINAL BACKGROUND OF THE INVENTION 1. Field of the Invention Thisinvention relates to a method and apparatus for making multiple copiesfrom an original, and more particularly a method of making multiplecopies from a first original by formation of a temporary image so thatthe first original can be replaced by a second original while copies arebeing made of the first original from the temporary image.

2. Description of the Prior Art Toward the end of the 19th Century F.Reinitzer and O. Lehmann independently observed that certain substancesin passing from a solid crystalline state to an isotropic liquid statepass through a state or condition over a given temperature range whereinthey display rheological properties similar to that of fluids, but haveoptical properties similar to that of the crystalline state. In order toidentify these properties, Lehmann used the term liquid crystal, whichterminology persists today. Present thinking tends to regard substanceswhich exhibit these properties as being in a fourth state of matterknown as the mesomorphic state or mesophase since it is a state or phaseintermediate that of the anisotropic crystal and that of the isotropicliquid.

There are three distinct mesomorphic states or forms, namely, thesmectic mesophase, the nematic mesophase and the cholesteric mesophase.A nematic liquid crystal is essentially transparent, and thereforetransmits light, but when placed in a d.c. electric field the moleculesof some of these liquid crystals become disoriented so that the materialdiffuses light and becomes milky white in appearance. When the d.c.electric field is removed, the molecules of the liquid crystal return totheir previous orientation so that the liquid crystal is againtransparent. This phenomena is discussed in PROCEEDINGS OF THE I.E.E.E.,for July, 1968 in an article entitled: Dynamic Scattering: A newElectro-optical Effect in Certain Classes of Nematic Liquid Crystals",By Heilmeier, Zanoni and Barton at pages 1162-1171.

The reflective optical storage effect of mixtures of cholesteric andnematic liquid crystal materials is discussed in a paper appearing inAPPLIEDPHYSICS LETTERS for Aug. 15, 1968 in an article entitled, A NewElectric Field Controlled Reflective Optical Storage Effect inMixed-Liquid Crystal Systems, by Heilmeier and Goldmacher at pages 132and 133, in which the authors described how a mixture of nematic andcholesteric mesomorphic materials serve as an optical storage under ad.c. or low frequency a.c. electric field, which changes the intiallytransparent material to a milky white light-diffusing material. Theliquid crystal material remains in the light-diffusing state uponremoval of the dc. field. The mixture can be rapidly erased or changedback to a transparent state by the application of a high frequency a.c.signal greater than 700 Hz.

U.S. Pat. No. 2,892,380 to Baumann et a1 describes a schlieren-opticalsystem for amplifying the light intensity of an optically projectedimage. A multiple layer control cell, consisting of a liquid crystallayer and a photoconductive layer, is bounded by a pair of electrodeswhich are connected to a d.c. source. The liquid crystal layer is a typewhich has an electric Kerr effect.

An electrically nonconductive mirror is arranged between thephotoconductive and liquid crystal layers to provide optical isolationbetween a light image and a secondary light source. The light image israstered on the photoconductive layer so that it becomes conductive inthose areas where light strikes it. This produces a nonhomogeneouselectric field between the electrodes corresponding to the light imagewhich results in local variations in the index of refraction of theliquid crystal material corresponding to the light image. Light from asecondary source is reflected from the nonconducting mirror surface inaccordance with the image pattern on the liquid crystal and is projectedonto a screen to form a visible image.

In many document copy machines, if multiple copies of an original are tobe made, it is necessary to reexpose the original for each subsequentcopy that is desired. Thus, after the last copy of an original is madethere is a time delay while the first original is moved out of theexposure station and a second original is brought into the exposurestation which imposes severe restrictions on machine speed. In someapparatus, an image of an original is projected onto a photosensitivesurface which is developed to form a temporary image and this image inturn is projected onto a photosensitive receiver to form a copy. Such anapparatus is disclosed in U.S. Pat. No. 3,504,969 to R. W. Martel.However, this apparatus suffers the same shortcoming as the apparatusdescribed above in that to make multiple copies, the original must beexposed once for each copy. Thus, when a new original is to be exposed atime delay is experienced while the first original is removed and asecond original is positioned.

SUMMARY OF THE INVENTION.

In accordance with this invention, a method is provided comprising thesteps of: forming a first temporary erasable image from a firstoriginal, exposing a first photosensitive surface at an exposure stationto the first temporary image to form a latent image on the firstphotosensitive surface, removing the first photosensitive surface fromthe exposure station for development, positioning a secondphotosensitive surface at the exposure station for'exposure and exposingthe second photosensitive surface to the first temporary image to form alatent image on the second photosensitive surface. Exposure ofsubsequent photsensitive surfaces can continue until the desired numberof copies are made. While multiple copies of the first original arebeing made a second original can be positioned for making a secondtemporary image. This method can be accomplished by means for formingsuccessive erasable temporary images from a plurality of originals,means for exposing each of a plurality of photosensitive surfacessequentially to each temporary image to form a plurality of latentimages, and means for erasing each temporary image after a predeterminednumber of latent images have been made.

In one embodiment, the method of this invention is carried out byapparatus which includes a layered sandwich structure on which atemporary image can be formed. This layer structure includes, in order,a first transparent electrode, a photoconductive layer, a liquid crystallayer, and a second transparent electrode. Means are provided for applya d.c. potential between the electrodes while a radiation patterncorresponding to the first original is projected by a first source ofelectromagnetic radiation onto the photoconductive layer to form a firsttemporary image on the liquid crystal layer. Means is provided forprojecting the temporary image by a second source of electromagneticradiation onto a photosensitive surface at an exposure station, such asa photoconductive member movable along an endless path past a series ofelectrophotographic stations after the potential across the electrodesis removed. Control means is provided which is responsive to projectionof the temporary image to move a first original out of a projectionplane and position a second original and which is further responsiveafter a predetermined exposure time sequentially to disable thetemporary image projection means and to move the exposed photoconductivemember to a developing station and to bring a second charged portion ofthe photoconductive member from a charging station into the exposurestation and to project the temporary image onto the second chargedportion of the photoconductive member to make a second copy.

Additional advantages of this invention will become apparent from thedescription which follows, taken in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematicrepresentation of one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with thisinvention, a temporary image is formed on a photoconductive-liquidcrystal sandwich S, by projection of an image of an original by a firstlight source, which temporary image is projected by a second lightsource onto a photosensitive surface or material, such as aphotoconductive belt 2 mounted to be driven along an endless path by amotor 4 past a charging station 6, an exposure station 8, a developingstation 10, a transfer station 12, and a cleaning station 14. p

The photoconductive-liquid crystal sandwich S comprises in order: afirst transparent electrode 16, a transparent photoconductive layer 18,a control layer, such as a liquid crystal layer 20, and a secondtransparent electrode 22. A potential can be applied across electrode 16and 22 by switch 24 which can be connected either to d.c. potentialsource 26 to form a temporary image in the liquid crystal layer or toac. potential source 28 to erase the temporary image on theliquidcrystal layer as will be more fully understood from thedescription below.

An original, such as film 30, is fed from a supply roll 32 to a takeuproll 34 through film guides 36 which define a projection plane and alignsuccessive film frames or images in an exposure position during movementof the film. The film may be incrementally advanced as by motor 38, asdescribed below, to position seriatim successive original images to beprojected. An image on the original is projected, as by a firstillumination source, such as lamp 40. This original image is projectedby lens 42 through an aperture 44, which is normally closed by a shutter46, onto a beam splitter 48 which reflects the image from original 30through transparent electrode 16 and onto photoconductive layer 18,while d.c. potential 26 is applied across electrodes l6 and 22 toestablish an electric field therebetween. The photoconductive layer willact as though it is more conductive in the areas which are illuminatedthan it will in unilluminated areas so that a greater portion of theelectric field is across corresponding portions of the liquid crystal 20causing such portions to diffuse any light striking them thereby forminga temporary image corresponding to the original. A potential of 400volts applied for 0.5 seconds has been found to satisfactorily form thetemporary image.

A suitable liquid crystal material is a mixture of a nematic mesophase,such as N-[P-Methoxybenzylidene]- p-Butylaniline and a cholestericmesophase of cholesteryl oleyl carbonate, wherein the mixture is 10parts by weight of nematic mosophase to one part cholesteric mesophase.The photoconductive material can be 4, 4'-diethylamino2,2--dimethyltriphenol methane and a polycarbonate resin together with apyrylium dye prepared as in Example I of British Pat. No. 1,153,506issued Sept. 29, 1969.

When the image is no longer needed, switch 24 is moved to bringalternating potential source 28 into the circuit, such as 600 volts at afrequency of 1000 Hz for one or two seconds, to return the liquidcrystal layer to its quiescent or transparent state.

A suitable thickness for the liquid crystal layer is 12 microns and is10 microns for the photoconductive layer. The two layers convenientlyare separated by a layer of cellulose nitrate of one micron or less inthickness which layer is to inhibit adverse chemical reactions betweenthe liquid crystal material and the photoconductive material. I

The temporary image which is formed on liquid crystal layer 20 may beprojected by a second illumination source, such as lamp 50. Radiationfrom lamp 50 passes through beam splitter 48 so that the image on theliquid crystal is projected by field lens 52 and objective lens 54,through aperture 56, normally closed by shutter 58, onto a chargedportion of photoconductive web 2. Alternatively, beam splitter 48 can bereplaced by a plane mirror which will reflect the image of the originalonto the photoconductive-liquid crystal sandwich to form the temporaryimage and can be moved out of the optical path when the temporary imageis to be projected by lamp 50.

While a temporary image is being projected to make multiple copies asecond original can be positioned. If desired, a viewing screen, notshown, can be provided along with suitable apparatus for searchingthrough a film supply for a particular image from which subsequentprints are to be made.

This invention has particular application as an exposure station for anelectrophotographic device in which it is desired to make multiplecopies from an original. By means of the present invention an image ofthe original may be projected a single time onto thephotoconductive-liquid crystal sandwich S to form a temporary imagewhich in turn may be projected to exposure sequentially a plurality ofcharged photosensitive surfaces as they are moved through the exposurestation and while another original is being positioned. As used herein,the term photosensitive surface, is intended to denote a segment ofendless photoconductive belt 2 which is of sufficient size to receive animage projected from a photoconductive-liquid crystal structure S. Itwill also be understood that the term is also applicable to a continuousweb of photosensitive material fed from a supply roll to a take-up rollor to cut sheets of photosensitive paper.

Referring now to the logic and control circuit, which is illustrated inthe drawing by standard symbols as disclosed in American StandardGraphic Symbols For Logic Diagrams (ASA Y32.l4-1962), published by theAmerical Institute of Electrical Engineers, the apparatus may include anarbitrary number counter 60 which the operator sets to a selected numberrepresentative of the number of prints or copies desired. Thereafter,the operator presses a print button 61 to energize the counter whereupona signal is generated at the one" output of the counter to provide asignal to AND gate 62. Another input to AND gate 62 is provided by aswitch 64 which is positioned to be closed when an original such as film30 is in position in film guides 36 for projection. Switch 64 isconnected to a potential source 66 which in turn is connected to ground.The third input to AND gate 62 is provided when lamp 50 is notenergized. Thus, if the print button has been depressed, the film is inthe gate and light 50 is not on, as would be the case when initialoperation of the machine begins, AND gate 62 is enabled to provide anoutput signal to single shot generator 68 which in turn provides asignal of a predetermined limited time duration to lamp 40 and to asolenoid 70 which opens shutter 46 to expose the photoconductive layerof the sandwich structure S to film 30. The signal from single shotgenerator 68 also sets flip-flop 71, so that a signal is provided fromits one output, and energizes solenoid 72 to move switch 24 to apply thed.c. potential of source 26 across electrode 16 and 22 to create anelectric field therebetween to form a temporary image on liquid crystallayer in response to the exposure of the photoconductive layer 18, asdescribed above. Conveniently, means (not shown) can be provided to varyexposure time, as required. Upon termination of the signal from singleshot generator 68, AND gate 74, which has one input connected to the oneterminal of counter 60 and a second input connected to single shotgenerator 68, is enabled to provide a signal to energize lamp 50 toproject the temporary image on liquid crystal layer 20 onto a chargedportion of photoconductive belt 2 in exposure station 8. This signalfrom AND gate 74 also enables AND gate 76 to provide a signal to singleshot generator 78 which energizes solenoid 79 for a predetermined timeto open shutter 58 to permit exposure of the photoconductive web to thetemporary image. The exposure time can be varied by means (not shown),as required. During the exposure of photoconductive web 2, the samesignal form AND gate 75 enables AND gate 80 which receives input signalsfrom flip-flop 71 and protential source 66 if switch 64 is closed tosupply a signal to single shot generator 81. Single shot generator 81provides a signal which energizes motor 38 to advance the next originalinto exposure position and to clear flipflop 71. Advantageously, theoriginal is advanced during projection of the first temporary image. Thesignal from single shot generator 78 also is fed back to counter 60 toindicate that one of the selected number of prints has been made. Thissame signal is fed to the set terminal of flip-flop 82 and flip-flop 84.Thus, flipflop 82 provides a signal to AND gate 86 which in turnprovides a signal to a single shot generator 88 as soon as the signalfrom single shot generator 78 has terminated. The signal from singleshot generator 88 energizes motor 4 so that photoconductive web 2 isadvanced an incremental distance to bring the next charged section intothe exposure station for subsequent exposure to the temporary image toform the next electrostatic latent image. In this way, thephotoconductive surfaces are fed seriatim through exposure station 8.

It will be understood that after each incremental advance of motor 4 dueto a signal from single shot generator 88, a signal is provided to ANDgate 76 which will terminate the output signal therefrom. Upontermination of the signal from single shot generator 88, AND gate 76provides another output signal to single shot generator 78 if there isstill a signal from the one input of counter 60 so that solenoid 79 willbe energized again to open shutter 58 and make another exposure. Thissequence will continue until an exposure for the last of the number ofprints to be made from a particular original has been made. Thus, thephotoconductive surfaces are advanced seriatim through exposure station8 for exposure. When the last exposure is made, the signal from singleshot generator 78 causes an output signal to be generated from zerooutput of counter 60 which in turn cause several things to occur. Firstof all, the zero signal is supplied to an AND gate 90 which has anotherinput connected to flip-flop 84 which was previously set by a signalfrom single shot generator 78 so that AND gate 90 now provides a signalthrough normally closed switch 92 to motor 4 so that the motor continuesto run until the last image has been transferred at transfer station 12whereupon means (not shown) will open switch 92 to stop the motor. Whenthe signal to motor 4 is interrupted AND gate 94 will provide a signalto clear flip-flop 84. In addition, the signal from the zero output ofcounter 60 provides a signal to single shot generator 96 to operatesolenoid 98 to connect switch 24 to ac. source 28 momentarily to erasethe temporary image on liquid crystal layer 20 and then return switch 24to the intermediate position shown. This zero signal from counter 60 canalso be used to discontinue charging of subsequent photoconductivesurfaces, by means not shown. At this point, all operations of theapparatus stop and the apparatus is in condition for making prints froma second original, which has already been positioned, when the operatorsets the number of prints desired on counter 60 and presses the printbutton to initiate the cycle as previously described.

From the foregoing, the advantages of this invention are readilyapparent. A method and apparatus has been provided wherein multipleprints may be made from a temporary image which is formed by a singleexposure to an original. This facilitates the removal of a firstoriginal from an exposure gate and the positioning of a second originalduring the time that one or more copies are made from the firsttemporary image to provide a device which can be recycled rapidly tomake copies from other originals.

It will be understood that different circuitry could be used than thatdisclosed and that if it is desired to project both the original imageand the temporary image simultaneously, a photoconductive layer for theliquid crystal sandwich structure must be chosen which is sensitive toalimited portion of the electromagnetic spectrum such as ultravioletlight in which case lamp 40 would be ultraviolet. In this case, thetemporary image can be projected by white light. In this case, asuitable photoconductive material is poly-N-vinylcarbozole ortriphenylamine dispersed in a poly-styrene vehicle. One

suitable nematic liquid crystal material comprises 80 mol percent ofButyl p-(p-ethoxyphenoxycarbonyl)- phenyl carbonate and mol percent ofp-[N-(pmethoxybenzylidene) amino] phenyl acetate. This material is amesophase between 42C and 52C. Another suitable material is made upone-third by weight of each of P-l(p-methoxybenzylidene) amino] phenylacetate; p-(p-methoxybenzylidene) amino butyrate; andp-(p-butoxybenzylidene) amino acetate which is a mesophase between C and55C. Other suitable materials are listed on pp. 11-13 of MolecularStructure and the Properties of Liquid Crystals by G. W. Grey (1962).Since nematic liquid crystal layers will retain an image only so long asa potential is applied across them, it is necessary to maintain switch24 in circuit with d.c. potential 26, such as 250 to 400 volts, as longas the temporary image on the liquid crystal is to be projected. Otherranges of electromagnetic radiation can be selected so long as thephotosensitive surface upon which a latent image is to be made issensitive to a particular range of the electromagnetic spectrum which isused to project the temporary image.

The invention has been described in detail with reference to a preferredembodiment thereof, but it will be understood that variations andmodifications can be effected within the spirit and scope of theinvention.

I claim:

1. Apparatus for forming multiple images of each of a plurality oforiginals sequentially on a plurality of photosensitive surfaces at anexposure station, said apparatus comprising:

means for successively forming an erasable, temporary image from each ofthe plurality of originals, said forming means including:

a layered sandwich structure having in order,

a first transparent electrode,

a transparent photoconductive layer,

a control layer which is substantially transparent in the absence of anelectric field and scatters light under the influence of an electricfield, and

a second transparent electrode,

means for applying a potential between said electrodes to create anelectric field therebetween, and

means for exposing said photoconductive layer through said firsttransparent electrode to each of said originals to render saidphotoconductive layer more conductive in exposed areas to increase theelectric field across correspponding portions of said control layer toform said temporary image of the original on said control layer;

activatable means for exposing sequentially each of a plurality ofphotosensitive surfaces to each temporary image to form a latent image;and

means for erasing each temporary image after projection thereof ontoeach of said plurality of photosensitive surfaces.

2. Apparatus, as claimed in claim 1, further includneans for advancingsaid photosensitive surfaces seriatim into and out of the exposurestation in response to termination of exposure of each saidphotosensitive surface in the exposure station.

3. Apparatus, as claimed in claim 2, further including:

means for activating said exposing means in response to advancement ofsaid photosensitive surfaces.

4. Apparatus, as claimed in claim 1, wherein said temporary imageforming means includes:

means for positioning each original to form each temporary image; and

means for advancing said originals seriatim into and out of saidpositioning means in response to formation of a temporary image of anoriginal in said positioning means.

5. Apparatus, as claimed in claim 1, wherein said control layercomprises:

liquid crystal material.

1 6. Apparatus, as claimed in claim 1, further including:

means for disabling said potential applying means after formation of atemporary image.

7. Apparatus for making multiple images sequentially on successivephotosensitive surfaces in an exposure station from a temporary erasableimage formed from a single exposure to an original, said apparatuscomprising:

a layered sandwich structure which includes in order:

a first transparent electrode;

a transparent photoconductive layer; a liquid crystal layer; and

a second transparent electrode;

a first source of potential for application across said electrodes atleast during formation of said temporary image;

means selectively operable to apply said first source of potentialacross said transparent electrodes at least during formation of saidtemporary erasable image;

means for exposing said photoconductive layer to a radiation patterncorresponding to a first original for a predetermined exposure time whensaid first potential is applied across said electrodes to form a firsttemporary image on said liquid crystal layer;

means for projecting radiation through said layered sandwich structureto expose a first photosensitive surface in the exposure station to saidfirst temporary image to form a corresponding latent image on said firstphotosensitive surface;

control means for enabling said operable means during exposure to saidradiation pattern and responsive after a predetermined exposure timesequentially; to disable said means for projecting radiation to move anexposed photosensitive surface out of the exposure station and move anunexposed photosensitive surface into the exposure station, and toenable said means for projecting radiation to expose said unexposedphotosensitive surface to said first temporary image to form acorresponding latent image on said second photosensitive surface.

8. Apparatus, as claimed in claim 7, wherein said control means furtherincludes:

means to disable said operable means upon formation of said temporaryimage.

9. Apparatus, as claimed in claim 8, further includa second source ofpotential for application across said electrodes to erase said temporaryimage; and wherein said operable means is also operable to apply saidsecond source. of potential across said electrodes, said control meansfurther including:

means to enable said operable means to apply said second potentialacross said electrods upon exposure of a predetermined number ofphotosensitive surfaces to said temporary image.

10. Apparatus, as claimed in claim 9, wherein:

said first source of potential is a d.c. source, and

said second source of potential is an a.c. source.

11. Apparatus as claimed in claim 7 further including:

means responsive to exposure to said first temporary image for movingsaid first original out of said projection plane and for moving a secondoriginal into said projection plane.

12. Apparatus for making multiple copies sequentially on photosensitivematerial in an exposure station from an original which is removableduring sequential exposure of the photosensitive material forreplacement by another original from which one or more copies are to bemade, said apparatus comprising:

a layered sandwich structure that is capable of having a temporary imageformed therein, which sandwich structure includes in order:

a first transparent electrode; a transparent photoconductive layer; aliquid crystal layer; and

a second transparent electrode;

a first source of potential connectable across said electrodes;

a switch operable to connect said electodes across said first potentialsource at least during formation of said temporary image;

original advancing means for moving originals seriatim into and out ofsaid projection plane;

means for exposing said photoconductive layer to a radiation pattern ofan original and for enabling said switch to apply said first potentialacross said electrodes at least during formation of the temporary imageof the original in said liquid crystal layer;

means for moving photosensitive material seriatim into and out of theexposure station;

means for projecting radiation in response to formation of saidtemporary image through said sandwich structure to expose photosensitivematerial in the exposure station to said temporary image;

means responsive to said radiation projecting means to enable saidoriginal advancing means to bring another original into said projectionplane while said temporary image is being projected;

means for enabling said photosensitive material moving means in responseto exposure of the photosensitive material in the exposure station tomove the exposed photosensitive material out of the exposure station andposition unexposed photosensitive material in the exposure station;

counting means having a first input for selecting the number of copiesto be made from an original, and having a second input for receiving acount signal each time photosensitive material is exposed to a temporaryimage, said counting means providing a first signal until the selectednumber of copies have been made; and

means for enabling said exposing means and for providing said countsignal to said second input of said counting means in response topositioning of exposed photosensitive material in the exposure stationand in response to said first signal from said counting means,

13. Apparatus, as claimed in claim 12, wherein said liquid crystal layeris a mixture of nematic and cholesteric material having a memory andsaid countingmeans provides a second signal when the selected number ofcopies have been made, said apparatus further including:

a second source of potential connectable across said electrodes to erasesaid temporary image;

means responsive to said second signal from said counting means toenable said switch to connect said electrodes across said secondpotential source to erase the temporary image in said liquid crystallayer.

14. In an electrophotographic apparatus which includes a photoconductivemember movable along an endless path past a plurality of stations spacedalong said path, said plurality of stations including: a chargingstation for placing a generally uniform electrostatic charge on saidphotoconductive member; an exposure station for exposing a chargedportion of said photoconductive member to a pattern of radiation derivedfrom an original to form an electrostatic latent image; a developingstation for developing said electrostatic latent image to form a tonerimage; a transfer station to transfer the toner image to a receiver; anda cleaning station for removing residual toner particles from saidphotoconductive member, and activatable means for moving saidphotoconductive member along said endless path, the improvement in saidexposure station comprising:

a layered sandwich structure which includes in order:

a first transparent electrode;

a photoconductive layer;

a liquid crystal layer; and

a second transparent electrode;

means for applying a first potential between said electrodes;

means for exposing said photoconductive layer to a radiation pattern fora predetermined exposure time while said first potential is appliedacross said electrodes to render exposured areas of said photoconductivelayer more conductive than unexposed areas thereof to form a firsttemporary image on said liquid crystal layer;

means for projecting radiation through said layered sandwich structureto exposure a first charged portion of said photoconductive member insaid exposure station to said first temporary image to form acorresponding electrostatic latent image on said first charged portion;

control means responsive after a predetermined exposure timesequentially to disable said means for projecting said radiation withinsaid second portion of the electromagnetic specturm, to activate saidmeans for moving said photoconductive member to move the exposed portionfromthe exposure station to the developing station and to move a secondcharged portion from the charging station to the exposure station, andto enable said means for projecting radiation to expose said secondcharged portion of said photoconductive member to said first temporaryimage to form a corresponding electrostatic latent image on said secondcharged portion of said photoconductive member.

15. The improvement, as claimed in claim 14, further including:

means for applying a second source of potential across said electrodesfor erasing said temporary image after a predetermined number ofexposures of successive portions of said photoconductive member.

1. Apparatus for forming multiple images of each of a plurality oforiginals sequentially on a plurality of photosensitive surfaces at anexposure station, said apparatus comprising: means for successivelyforming an erasable, temporary image from each of the plurality oforiginals, said forming means including: a layered sandwich structurehaving in order, a first transparent electrode, a transparentphotoconductive layer, a control layer which is substantiallytransparent in the absence of an electric field and scatters light underthe influence of an electric field, and a second transparent electrode,means for applying a potential between said electrodes to create anelectric field therebetween, and means for exposing said photoconductivelayer through said first transparent electrode to each of said originalsto render said photoconductive layer more conductive in exposed areas toincrease the electric field across correspponding portions of saidcontrol layer to form said temporary image of the original on saidcontrol layer; activatable means for exposing sequentially each of aplurality of photosensitive surfaces to each temporary image to form alatent image; and means for erasing each temporary image afterprojection thereof onto each of said plurality of photosensitivesurfaces.
 2. Apparatus, as claimed in claim 1, further including: meansfor advancing said photosensitive surfaces seriatim into and out of theexposure station in response to termination of exposure of each saidphotosensitive surface in the exposure station.
 3. Apparatus, as claimedin claim 2, further including: means for activating said exposing meansin response to advancement of said photosensitive surfaces. 4.Apparatus, as claimed in claim 1, wherein said temporary image formingmeans includes: means for positioning each original to form eachtemporary image; and means for advancing said originals seriatim intoand out of said positioning means in response to formation of atemporary image of an original in said positioning means.
 5. Apparatus,as claimed in claim 1, wherein said control layer comprises: liquidcrystal material.
 6. Apparatus, as claimed in claim 1, furtherincluding: means for disabling said potential applying means afterformation of a temporary image.
 7. Apparatus for making multiple imagessequentially on successive photosensitive surfaces in an exposurestation from a temporary erasable image formed from a single exposure toan original, said apparatus comprising: a layered sandwich structurewhich includes in order: a first transparent electrode; a transparentphotoconductive layer; a liquid crystal layer; and a second transparentelectrode; a first source of potential for application across saidelectrodes at least during formation of said temporary image; meansselectively operable to apply said first source of potential across saidtransparent electrodes at least during formation of said temporaryerasable image; means for exposing said photoconductive layer to aradiation pattern corresponding to a first original for a predeterminedexposure time when said first potential is applied across saidelectrodes to form a first temporary image on said liquid crystal layer;means for projecting radiation through said layered sandwich structureto expose a first photosensitive surface in the exposure station to saidfirst temporary image to form a corresponding latent image on said firstphotosensitive surface; control means for enabling said operable meansduring exposure to said radiation pattern and responsive after apredetermined exposure time sequentially: to disable said means forprojecting radiation to move an exposed photosensitive surface out ofthe exposure station and move an unexposed photosensitive surface intOthe exposure station, and to enable said means for projecting radiationto expose said unexposed photosensitive surface to said first temporaryimage to form a corresponding latent image on said second photosensitivesurface.
 8. Apparatus, as claimed in claim 7, wherein said control meansfurther includes: means to disable said operable means upon formation ofsaid temporary image.
 9. Apparatus, as claimed in claim 8, furtherincluding: a second source of potential for application across saidelectrodes to erase said temporary image; and wherein said operablemeans is also operable to apply said second source of potential acrosssaid electrodes, said control means further including: means to enablesaid operable means to apply said second potential across said electrodsupon exposure of a predetermined number of photosensitive surfaces tosaid temporary image.
 10. Apparatus, as claimed in claim 9, wherein:said first source of potential is a d.c. source, and said second sourceof potential is an a.c. source.
 11. Apparatus as claimed in claim 7further including: means responsive to exposure to said first temporaryimage for moving said first original out of said projection plane andfor moving a second original into said projection plane.
 12. Apparatusfor making multiple copies sequentially on photosensitive material in anexposure station from an original which is removable during sequentialexposure of the photosensitive material for replacement by anotheroriginal from which one or more copies are to be made, said apparatuscomprising: a layered sandwich structure that is capable of having atemporary image formed therein, which sandwich structure includes inorder: a first transparent electrode; a transparent photoconductivelayer; a liquid crystal layer; and a second transparent electrode; afirst source of potential connectable across said electrodes; a switchoperable to connect said electodes across said first potential source atleast during formation of said temporary image; original advancing meansfor moving originals seriatim into and out of said projection plane;means for exposing said photoconductive layer to a radiation pattern ofan original and for enabling said switch to apply said first potentialacross said electrodes at least during formation of the temporary imageof the original in said liquid crystal layer; means for movingphotosensitive material seriatim into and out of the exposure station;means for projecting radiation in response to formation of saidtemporary image through said sandwich structure to expose photosensitivematerial in the exposure station to said temporary image; meansresponsive to said radiation projecting means to enable said originaladvancing means to bring another original into said projection planewhile said temporary image is being projected; means for enabling saidphotosensitive material moving means in response to exposure of thephotosensitive material in the exposure station to move the exposedphotosensitive material out of the exposure station and positionunexposed photosensitive material in the exposure station; countingmeans having a first input for selecting the number of copies to be madefrom an original, and having a second input for receiving a count signaleach time photosensitive material is exposed to a temporary image, saidcounting means providing a first signal until the selected number ofcopies have been made; and means for enabling said exposing means andfor providing said count signal to said second input of said countingmeans in response to positioning of exposed photosensitive material inthe exposure station and in response to said first signal from saidcounting means.
 13. Apparatus, as claimed in claim 12, wherein saidliquid crystal layer is a mixture of nematic and cholesteric materialhaving a memory and said counting means provides a second signal whenthe sElected number of copies have been made, said apparatus furtherincluding: a second source of potential connectable across saidelectrodes to erase said temporary image; means responsive to saidsecond signal from said counting means to enable said switch to connectsaid electrodes across said second potential source to erase thetemporary image in said liquid crystal layer.
 14. In anelectrophotographic apparatus which includes a photoconductive membermovable along an endless path past a plurality of stations spaced alongsaid path, said plurality of stations including: a charging station forplacing a generally uniform electrostatic charge on said photoconductivemember; an exposure station for exposing a charged portion of saidphotoconductive member to a pattern of radiation derived from anoriginal to form an electrostatic latent image; a developing station fordeveloping said electrostatic latent image to form a toner image; atransfer station to transfer the toner image to a receiver; and acleaning station for removing residual toner particles from saidphotoconductive member, and activatable means for moving saidphotoconductive member along said endless path, the improvement in saidexposure station comprising: a layered sandwich structure which includesin order: a first transparent electrode; a photoconductive layer; aliquid crystal layer; and a second transparent electrode; means forapplying a first potential between said electrodes; means for exposingsaid photoconductive layer to a radiation pattern for a predeterminedexposure time while said first potential is applied across saidelectrodes to render exposured areas of said photoconductive layer moreconductive than unexposed areas thereof to form a first temporary imageon said liquid crystal layer; means for projecting radiation throughsaid layered sandwich structure to exposure a first charged portion ofsaid photoconductive member in said exposure station to said firsttemporary image to form a corresponding electrostatic latent image onsaid first charged portion; control means responsive after apredetermined exposure time sequentially to disable said means forprojecting said radiation within said second portion of theelectromagnetic specturm, to activate said means for moving saidphotoconductive member to move the exposed portion from the exposurestation to the developing station and to move a second charged portionfrom the charging station to the exposure station, and to enable saidmeans for projecting radiation to expose said second charged portion ofsaid photoconductive member to said first temporary image to form acorresponding electrostatic latent image on said second charged portionof said photoconductive member.
 15. The improvement, as claimed in claim14, further including: means for applying a second source of potentialacross said electrodes for erasing said temporary image after apredetermined number of exposures of successive portions of saidphotoconductive member.